Facebook introduced new requirements which means that you’ll have to install Planable app to your Facebook group. All you have to do is select the group, then click "Authorize" button and add Planable to your Facebook Group.
In case you still won't be able to create & publish posts for the Facebook Group, make sure to add Planable as an authorized app in your Facebook Group. And reconnect the page with an account that is an admin in the group.
Simply go to your group settings and search for Apps and add Planable.